As I wrote in an early post, many people are familiar with the basic Big Bang Theory: that the universe was born in a violent explosion. Beyond that popular conception is hazy, with a lot of people thinking the planets, stars, galaxies, asteroids and everything else popped into being fully formed.
If you had been present at the explosion there wouldn’t have been much to see. Unimaginable amounts of energy were released. It was pure chaos, with temperatures far too high to allow the energy to convert to matter (Einstein’s famous E = mc2 , where E stands for energy, m for mass and c for the speed of light shows that energy and matter are interchangeable). However, within about 300 seconds of the Big Bang the temperature had dropped to where lighter elements like hydrogen and helium could form. During the next critical minutes nuclei were formed. Once the universe cooled to about one million degrees C, nuclear fusion stopped. Matter existed in a state known as plasma. Most people are familiar with the first three phases, solid, liquid and gas. Hotter than gas, plasma is a state of matter in which the temperature is so high that atomic nuclei cannot hold onto electrons. This condition existed until the temperature dropped to about 3,000 C, which took about 300,000 years. At that point nuclei could hold onto electrons and elements began to form.
One other thing was present at the Big Bang: enormous amounts of light. Had you been there you wouldn’t have seen anything because light is scattered by plasma, just as it is scattered by water droplets in the air, which creates fog. Just as you can’t see in a car at night in fog because the fog scatters the light from your headlights, so would the light from the Big Bang have been scattered. For 300,000 years or so the universe was the proverbial pea soup.
After 300,000 or so years the temperature was low enough to form elements, which are electrically neutral. Light doesn’t interact with neutral elements so it could pass unhindered through the universe for the first time.
Two scientists, George Gamow and Robert Herman, had been working on proving the Big Bang Theory. They suddenly realized that if the Big Bang Theory was correct and the theory about plasma cooling to allow formation of atoms, which in turn allowed light to pass unimpeded through the universe, the remnants of that light should still be visible today. If it could be detected it would further prove then validity of the Big Bang Theory. In fact, detection of this luminoues echo of the Big Bang would be almost conclusive proof of the Theory. Conversely, if the light wasn’t found the Big Bang couldn’t have happened.